HF links (the acronym standing for High-Frequency, situated between 3 MHz and 30 MHz) offer a non-line-of-sight communication capacity making it possible to carry out communications at long, or indeed very long distance, without requiring recourse to a satellite or to relay stations.
Hence, HF band communications use the reflection properties of the ionospheric layers for these frequencies. The drawback of the use of this band stems from the fact that, depending on the position of the ionospheric layers, propagation quality is not identical over the whole of the band. Thus, the HF band is generally divided into channels, thereby making it possible to allocate the frequency resource to various users, to afford frequency diversity to a communication, and also to adapt the use of the frequency resource to the transmission quality of the various channels, this quality varying as a function of time of day and geographical position.
Among the communication norms which use the HF band, the MIL STD 188-110C annex F standard, or the proposed STANAG 4539 annex H standard, describe the employment of several distinct 3 kHz channels for communicating. The invention lies in particular within the framework of transmissions of this type, using several 3 kHz channels, but also within the framework of multichannel transmissions using channels of greater width, such as for example in annex D of the MIL STD 188-110C standard, in the HF band or in other frequency bands.